Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$87.44	3.253%	$90.2844	$90.28	$90.30	$90.30
Purchase #2	$236.40	6.190%	$251.0332	$251.03	$251.05	$251.00
Purchase #3	$237.27	5.296%	$249.8358	$249.84	$249.85	$249.80
Purchase #4	$98.62	6.504%	$105.0342	$105.03	$105.05	$105.00
Purchase #5	$45.33	5.720%	$47.9229	$47.92	$47.90	$47.90
Purchase #6	$120.70	6.729%	$128.8219	$128.82	$128.80	$128.80
Purchase #7	$35.71	6.140%	$37.9026	$37.90	$37.90	$37.90
7 purchase totals =	$861.47		$910.8350	$910.82	$910.85	$910.70